Okay, we are tasked with adding 1620 and 8205. Let's begin!

Step 1: We'll start by adding the digits 0 & 5 in column 1 and get 5.

Step 2: We'll start by adding the digits 2 & 0 in column 2 and get 2.

Step 3: We'll start by adding the digits 6 & 2 in column 3 and get 8.

Step 4: We'll start by adding the digits 1 & 8 in column 4 and get 9.

So, 1620 + 8205 = 9825.

